
\begin{tikzpicture}[scale=2.4]
  \coordinate[label=left:$O$] (O) at (0,0);
  \coordinate[label=left:$A$] (A) at (180:1);
  \coordinate[label=right:$B$] (B) at (40:1);
  \coordinate[label=below:$C$] (C) at (-50:1);
  \coordinate[label=above:$D$] (D) at (90:1);
  \draw[name path=AB] (A) -- (B);
  \draw[name path=CD] (C) -- (D);
  \path[name intersections={of=AB and CD}]
    coordinate[label=below left:$P$] (P) at (intersection-1);
  \fill (O) circle (.5pt);
  \draw (O) circle (1);
\end{tikzpicture}
